The present invention relates to detonating systems used for perforating guns used in the oil field industry. A perforating gun is a device used to perforate oil and gas wells in preparation for well production. Such guns typically contain several shaped explosive charges and are available in a range of sizes and configurations. The diameter of the gun used is typically determined by the presence of wellbore restrictions or limitations imposed by the surface equipment. The perforating gun, fitted with shaped charges or bullets, is lowered to the desired depth in a well and fired to create penetrating holes in casing, cement, and formation. Thus, to perforate is to pierce the casing wall and cement of a wellbore to provide holes through which formation fluids may enter or to provide holes in the casing so that materials may be introduced into the annulus between the casing and the wall of the borehole.
In view of typical levels of electrostatic discharge, RF radiation, stray voltage, and/or accidental or unintended applications of power at the well-site, the switch and detonation system used for a perforating gun needs to be an RF safe system; otherwise, significant steps must be taken to render the well-site an RF free environment. As used herein, “RF safe” means that the switch and detonation system installed on the perforating gun is designed to be substantially immune to typical levels of electrostatic discharge, RF radiation, stray voltage, and/or accidental or unintended applications of power. An “RF safe environment” is an environment in which steps are taken to remove (or turn off) the components that generate electrostatic discharge, RF radiation, stray voltage, and applications of power nearby that would otherwise have interacted with the perforating gun (and its switch and detonation system). Conversely, a “non-RF safe environment” is an environment in which steps have not been taken to prevent typical levels of electrostatic discharge, RF radiation, stray voltage, and/or accidental or unintended applications of power. For example, an environment nearby the well-site at which the perforating gun is to be utilized in which steps have not been taken to prevent typical levels of electrostatic discharge, RF radiation, stray voltage, and/or accidental or unintended applications of power would be a “non-RF-safe environment” well-site.
Typical perforating gun systems use separate components for the pressure bulkhead, detonator, charge holder, detonation cord and wiring to the guns below. Historically, when a perforating gun is built, all the pieces are assembled together (except the detonator) and shipped to the location where the perforating operation is to be conducted. For example, a perforating gun can be made at a first location (e.g., a workshop, manufacturing site, testing facility or non-field location that is not the site at which perforating operations will be conducted) having a plurality of shaped charges having primer ends, a ballistics train including a detonating cord connected to the primer ends of the shaped charges, a detonator receptor that holds a booster and cord in place near a port, and wiring operatively connected between the ends of the gun tube and to the detonator receptor. One end of the detonating cord is also operatively connected to the detonator receptor. The detonator receptor can also include an addressable switch (or other intelligent switch) and a receptacle for receiving the detonator.
The gun tube assembled at the first location is then transported to a second location, which is the site at which the perforating operations will be conducted (e.g., a field location or other deployment site). It is at this second site that the detonator is installed to the perforating gun assembled at the first location. Generally, at that second location, the perforating gun is opened and the detonator is installed. RF-safe detonators (such as exploding foil initiators, exploding wire bridges, and semi-conductor bridges) are utilized to render the switch and detonator systems RF safe. The installation of the RF-safe detonator generally involves the utilization of a safety tube in which the RF-safe detonator is placed into before connection of the detonator to the wiring in the loading tube.
Examples of such RF-safe switch and detonator systems are discussed and described in U.S. Patent Appl. Pub. No. 2008/0202325, published Aug. 28, 2008, to Bertoja et al. By such use of the RF-safe detonator in the switch and detonator systems of the perforating gun, this avoids having to render the second location to be an RF free environment. Stated otherwise, until recently, the prior art taught that the detonator needed to be a RF-safe detonator or the environment needed to be an RF free environment, in order to protect against accidental detonation that could occur due to typical levels of electrostatic discharge, RF radiation, stray voltage, and/or accidental or unintended applications of power. See, e.g., U.S. Pat. No. 7,762,331, issued Jul. 22, 2010, to Goodman et al.
Recently, Hunting Titan has fabricated an RF-safe switch and detonator system that does not require the detonator to be an RF-safe detonator. This is done by combining (a) an addressable switch (such as Hunting Titan's ControlFire switch); (b) a standard detonator (such as an Austin Powder resistorized detonator having a minimum resistance of 50Ω); and a shunt switch. This combination system (which Hunting Titan refers to as its RF-Safe ControlFire-System) is assembled together with the shunt switch being set in the shorted position. The perforating gun is prepared at the first location independent of the RF-Safe ControlFire-System (and its three components). Since the addressable switch is part of the RF-Safe ControlFire-System, the addressable switch is not included within the perforating gun during this assembly at the first location.
After transport to the second location, the RF-Safe ControlFire System is then installed onto the perforating gun. Again, this requires connecting the addressable switch to the perforating gun at the second location. The shunt switch (which is part of the RF-Safe ControlFire System) is then turned to the non-shorted/armed position so that that the detonator system can then be installed onto the detonation cord (at which time the perforating gun is ready to be sent downhole for use).
While the RF-Safe ControlFire System utilizes a more reliable and more economical resistorized detonator (as compared with RF-safe detonators), this system has a significant drawback because this system requires that the addressable switch be installed at the second location, rather than the first. Because of this, the perforating gun is not testable at the first location (e.g., workshop, manufacturing site, testing facility). U.S. Pat. No. 2,953,971, issued Sep. 27, 1960, to Porter, shows the importance of being able to test at a location remote from the wellsite to enhance the margin of safety.
Testing at the first location is desirable because efficiencies and reliability are gained because, for example, any problems with the perforating gun can be identified and repair (or components replaced) before bringing the perforating gun to the well-site. Furthermore, such testing at the first location significantly reduces that there will be problems with the perforating gun at the second location. Indeed, if problems are identified at the second location, it may require returning the perforating gun back to the first location for repair or replacement or, alternatively, will require attempts to repair the perforating gun on-site with only a subset of equipment and parts that are back at the first location. Hence, it is safer and more economical to be able to test the perforating gun at the first location, something that cannot be done when using the RF-Safe ControlFire System.
Accordingly, there is a need for a method to create a RF-safe switch and detonator system that can utilize the more efficient and reliable resistorized detonators (rather than RF-safe detonators), while still affording the perforating gun to be assembled and tested at the first location before safely transporting the perforating gun to the well-site for use.